Although chemotherapy is an important treatment modality for advanced cancers, many anti-cancer drugs have limited therapeutic efficacy due to high systemic toxicity and lack of tumor selectivity. Several non-toxic prodrugs (e.g., glucuronide prodrugs) have been developed. These prodrugs, when converted to active drugs at a tumor site, exert high chemotherapy efficacy.
Typically, a prodrug is metabolized in vivo, preferably at the tumor site, to an active drug via enzyme digestion. Human lysosomal hydrolases (e.g., beta-glucuronidase) are ideal enzymes for use in prodrug therapy as they do not induce immune responses in human patients. However, the use is hindered by the low activity of these enzymes at physiological pH.
It has been of great interest to identify hydrolase variants that preserve enzymatic activity under physiological conditions, such as neutral pH.